ALT BUST.

Narrative

THE EVENT OCCURRED WHILE CLBING LEAR JET 35A OUT OF READING; PA. WE WERE HANDED OFF TO NEW YORK CTR BY HARRISBURG APCH AT 8000 FT. NEW YORK CTR CLBED US TO 10000 FT. THEY THEN GAVE US A HDG OF 360 DEGS AND A CLB TO 17000 FT EXPEDITE OUT OF 12000 FT. WE THEN WERE GIVEN 330. I UNDERSTOOD IT AS AN ALT AND SET 330 FT IN ALT ALERTER INSTEAD OF A HDG CHANGE TO 330 DEGS. I DID NOT REALIZE THERE WAS A PROB UNTIL CTR ASKED US TO VERIFY ALT. WE REPLIED FL210 CLBING TO FL330. HE THEN NOTIFIED US HE HAD ONLY CLRED US TO 17000 FT. HE ASKED US TO LEVEL AT 220. NO CONFLICT AROSE THAT WE KNOW OF. I AM NOT SURE WHETHER I READ BACK THE 330 CLRNC AS A HEADING OR ALT CLRNC. I THINK A FACTOR AFFECTING PERFORMANCE WAS FATIGUE DUE TO LENGTH OF DUTY DAY. WE MADE OUR 1ST DEP AT EARLY LCL AND HAD AWAKENED AT EARLIER FOR THIS. WE WERE ON OUR 4TH LEG OF THE DAY AT THE TIME OF THE OCCURRENCE. WE ALSO WERE CLBING AT ABOUT 3000 FPM DUE TO LIGHT WT; COLD AIR; AND EXPEDITE CLRNC. SUPPLEMENTAL INFO FROM ACN 261923: WE WERE GIVEN A CLB TO 17000 WHICH THE PIC IN THE R SEAT PLACED IN THE ALT SELECT OF THE AUTOPLT. SHORTLY THEREAFTER; WE WERE GIVEN A TURN TO A HDG OF 360 DEGS. THE NEXT TURN WAS GIVEN; AGAIN BY NEW YORK CTR TO 330 DEGS. AT THIS POINT I ROTATED THE HDG BUG TO 330 DEGS AND CONTINUED THE CLB -- WITH THE RATE OF CLB WE HAD I LOOKED TO THE ALT SELECT CTLR AND SAW THAT FL330 HAD BEEN SELECTED IN THE WINDOW. I ASSUMED I HAD MISUNDERSTOOD THE COMMAND; AND THAT WE WERE CLRED TO FL330.